Method and apparatus for electrolytic cutting, shaping, and grinding



March 11, 1958 G. F. KEELERIC 2,826,540

METHOD AND APPARATUS FOR ELECTROLYTIC CUTTING, SHAPING AND GRINDING Filed Sept. 18, 1952 2 Sheets-Sheet 1 lvr nngrs March 11, 1958 a. F. KEELERIC 2,826,540

METHOD AND APPARATUS FOR ELECTROLYTIC CUTTING, SHAPING AND GRINDING Filed Sept. 18, 1952 2 Sheets-Sheet 2 United States Patent 0 METHQD AND APPARATUS FOR ELECTRQLYTIC (IUTTHNG, SHAPING, AND GRlNDlNG George F. Keeleric, Evanston, ill.

Application September 18, 1952, Serial No. 33.65244 18 Claims. (Cl. 204-143) My invention relates to methods and apparatus for electrolytic cutting, shaping and grinding of very hard materials.

With the increased use of very hard materials in the form of alloys or in the form of sintered carbides like tungsten carbide in the making of tools and dies turbine buckets, ordnance, etc, the problem of economically cutting, shaping and grinding such materials is assuming great importance. The common method of performing such operations (which i will refer to generally hereinafter as shaping) is by the use of diamond abrasive wheels, flat or contoured as may be required. Diamond abrasive wheels are costly and the diamond bort used in their manufacture threatens to become very scarce in the face of its increased usage.

Among the objects of my invention are the following:

To shape hard niaterials with accurate control of dimensions, fine finishing, freedom from heat stressing or cracks or checks, and with minimum loss through defects;

To carry out such shaping operations at high speed,

safely, at low cost, and with a very low rate of wear on 3 grinding wheels or cathodes used in the process;

To provide apparatus which may be readily adaptable to the large quantity of costly grinding equipment already in use.

To achieve the above results it is my purpose to provide improvements in the electrolytic removal of material which may be augmened by the mechanical removal of insulating oxide films on the material to be shaped which interfere with electrolytic action. Where very high rates of removal are desired, 1 augment electrolytic action by abrasive action.

Another purpose of my invention is to provide control of the degree of sparking or arcing which occurs between the work to be shaped and the shaping electrode.

While the general phenomenon of electroylsis is wellknown, the principle has not hereto-fore been found applicable to the shaping of hard materials. Part of the reason for this fact lies in the slow removal rate provided by ordinary electrolytic methods, and part of the reason lies in the difliculty of getting accurate and smooth surface control. These are serious problems, for a practical method of shaping requires removal rates several hundred times greater than those encountered in such processes as electroplating and control of the surface on which removal is carried forward within a fraction of .001 inch.

If the attempt were made to increase the removal rate simply by increasing the voltage applied to the electrolytic circuit, the result would be to cause intolerable heating, gasing, and decomposition of the electrolyte as well as the wasteful dissipation of a very large amount of electric energy. This would also result in uneven and uncontrolled removal of material so that the remaining surface would be of little use for industrial purposes.

If the attempt is made to increase the removal rate by obtaining higher current through reducing the space he- 2,326,540 Fatenteel Mar. 11, 1958 2 tween the electrode and the material to be shaped, then two additional problems arise.

The first is that if the gap is narrowed sufiiciently to be useful, it is difficult to replenish the electrolyte within the gap at a sufiiciently rapid rate. The second is that with a narrow gap there is likelihood of serious sparking or arcing between the electrode and the material through the electrolyte. if heavy sparking occurs, it is likely to break over into arcing, and either the heavy sparking or arcing tends to produce a rough finish and damages the surface of the electrode. And, in any case, the problem of maintaining adequately close spacing is difficult, particularly in oil-hand grinding where the tool is simply supported on a tool rest and moved by hand in order to bring about the desired shaping.

By the means I have devised i am able to obtain a rate of material removal which is several hundred times the rates encountered in ordinary electrolytic processing. This may be illustrated by the fact that 1 am able to obtain current densities ranging from 200 amperes per square inch (of the surface of the material) up to more than 1000 amperes per square inch, whereas in ordinary electroplating, current densities will be of the order of l or 2 amperes per square inch. The rate of material removal is proportional to the current which is passed. At the same time, I am able to obtain a very smooth, even surface. The way in which I accomplish these results will be understood from the more detailed description of my invention which follows.

In the drawings:

Fig. l is a schematic representation of an embodiment of the mechanical apparatus used in my process and a circuit diagram of the electrical system; and

Fig. 2 is an elevation (partly in section) of an arrangement for indicating and controlling the pressure urging the work piece against the moving electrode.

Referring to 1, I will explain first the mechanical system used in my invention.

The mechanical apparatus may include a wide variety of commonly used grinding equipment. In the drawings a moving electrode 10 is mounted to a grinding shaft or spindle 11 through an electrically insulating bushing 13. The spindle or shaft may be driven by a motor 12, or in any other conventional manner.

The motor is mounted to a bed 14 which also carries a tool rest pedestal 1%. This is arranged in such a way that a tool to be ground may be rested on its upper surface and then moved by hand to achieve the desired shape. The tool proper frequently consists of a shank 17 to which a hardened tip 17a is attached, for example, by brazing. The tip 17a is frequently made of a hard metal carbide such as tungsten carbide, while the shank 17 is made of steel. One important feature of my invention is that the tip 17a and the shank 1'7 are shaped together in one operation, and are shaped evenly, so that it is not necessary to work separately on the tip and the shank. The tool consisting of the shank 1'7 and its attached tip 17a may be mounted in any conventional Way to a tool holder 16 which rests against the tool rest pedestal 15. It should be noted that good electric contact must be maintained between all of these elements-the tool, the tool holder, and the tool rest pedestal. Inasmuch as the electrolyte which is used is conductive and is necessarily splattered somewhat over this area, it is unnecessary to maintain polished surfaces, but the use of paint, etc., is to be avoided.

The arrangement of Fig. l for holding a tool in operative relationship to a moving electrode is suitable for off-hand grinding, but where a considerable number of identical tools is to be shaped, it is desirable to provide mechanical means for holding the tool with respect to the electrode. This mechanism is shown in Fig. 2.

for small Work pieces such as cutting tools l Referring to Fig. 2, the electrode 19 has abrasive insulating spacers mounted on its working surface. Electrode 1-45 is mounted to a rotating shaft ll through an insulating bushing 13. On the bed of a grinding ma chine, l provide ways 42 on which is slidably mounted a shoe 44 having guides Within guides 44:: a tool holder 16 is slidably mounted.

Tool holder 15 is fitted with a clamp member 46 and a clamping bolt 4-8 by which the work piece 17 with a hard tip 17a is clamped in position.

An air cylinder Ell is fastened by extending lugs and bolts 54 to shoe Within the cylinder 5b is mounted piston 5'6 which is connected through piston rod 58 to tool holder 16 by pin 69. At the head of the cylinder is a small airbleed hole 62.

One of the guides 44a is provided with a boss 6 which carries a stud 66 to make connection to pitman which is driven by a crank in the conventional manner. The crank 7t; may be turned by its cwnprirne mover or may be linked through speed reducing mechanism to motor 12.

The purpose of the crank mechanism and associated linkage is to give an oscillating motion to the work piec back and forth along the Working surface of electrode It In some cases, this is desirable in order that any Wear of the electrode t? or insulating spacers may be uniform across the working surface.

A flexible air supply tube 72, is connected to. the head of cylinder 5%. The air supply tube 72 is also fitted with a pressure gauge 74 and an adjustable pressure regulator 76 supplied from air supply line 73.

By setting the pressure regulator at the desired level, the amount of pressure urging the work piece 17 and 17a toward electrode against insulating spacers it? may be carefully adjusted and maintained. Ordinarily, prefer that the air cylinder be small, having a diameter of approximately one inch. The pressure regulator '76 may then be adjusted so as to sup ly very slight air pressure to the cylinder, thus putting very light force against the piston 56 so that the work piece makes firm but very light contact with insulating spacers It should be understood that the work piece may be movable and the electrode may be fixed. Or, as in rotary grinding where the work piece is circular in section, the Work piece may be rotated while the electrode also is rotated. Or the work piece may be moved back and forth along a stationary electrode as in a honing operation. What is important is that there be relative motion between the work piece and the electrode, and wherever I refer to a moving electrode 1 mean to include any means for achieving this relative motion.

An important feature of my invention lies in the use of insulating spacers by which very close spacing between the work piece 17 and 17a and the rotating or moving electrode 1% may be maintained. The use of insulating spacers in electric removal processes generally (e. g., the electrolytic method, the spark method, and the arc method) is describe..- in greater detail in my application for United States Letters Patent filed concurrently herewith and entitled Improvement in Electric Cutting, Shaping and Grinding, Serial No. 316,243, and now abandoned.

I prefer to hold a spacing distance under .001 inch and I have obtained good results with a spacing of .0007 inch, but even smaller spacing is permissible down to the point where actual contact between the work piece and the electrode is likely to occur through any irregularities in the system. The spacing is accomplished by interposing insulating spacers between the electrode and the work piece.

While many means of doing to mount the spacers the surface of this are available, I prefer more or less permanently on the electrode Fill. This may be done in several ways. For example, if hard abrasive particles are to be used as insulating spacers, they may be mounted to the electrode in the way described in my United States Letters Patent 2,368,472 for Method of Making Abrasive Articles, issued January 3Q, 1945. If insulating spacer particles are used which are less hard then they may be bonded to the electrode 10 and any irregularities in their protrusion may be eliminated by grinding with a line abrasive wheel so that all of the particles protrude the desired uniform distance outwardly from the metal electrode in.

Wi h whatever arrangement is used, care must be taken that a reasonable space is left between the particles, and this space on the electrode must be electrically conductive. This means either that the bonding material used must itself be conductive or that the presence of bonding material between the particles either be avoided at the time of application or removed by dissolving or etching or in some other way after the particles have been applied. I prefer not to occlude more than three-fourths of the working surface of the metal electrode 14 thus assuring adequate metal surface to serve as an electrode in the electrolytic process. if the entire surface of the electrode is covered by abrasive, it must be suilicientl pervious to provide channels for electrolyte adequate to carry the desi ed current.

The insulating spacers permit very close spacing, which is important not only in order to get requisite current densities, but also in controlling the dimensions and surface finish of the work. For example, if the space between the work piece and the moving electrode is opened up to as much as .605 inch, the surface generated on the work piece will be rough and uneven in contour, sometimes concave, sometimes convex. While this may not be troublesome for some kinds of operations, it is highly undesirable in making the final finish on dies and tools where the surfaces must be smooth and must follow the contour of the electrode. Here it should be un derstood that while I have shown an electrode having a flat surface, there will be many applications in which the electrode surface will be contoured to produce the desired shape on the work piece.

in the grinding of certain metals and metal carbides such as tungsten carbide, the abrasive insulating spacers 40, however applied, perform an additional important function which is the removal of an insulating oxide film which forms rapidly under electrolytic action. Since the film is soft, it may be removed easily and even the lightest direct contact betwen the work piece and the insulating spacers will bring about this result. But it must be removed if the electrolytic process is to go forward effectively.

It the insulating spacers are made of hard material, for example, diamond particles, then it is possible to accelerate the rate of material removal by pressing the work piece against the diamond particles with pressures used for ordinary diamond grinding. Under these conditions the electrolytic removal of material is augmented by abrasive action with the result that material is removed at a rate approximately 300 percent of the removal rate achieved by diamond grinding alone. Ordinarily, this augmentation will not be attempted with specialized contouring electrodes, for normal grinding pressures produce wear on the diamond particle surfaces (and removal of diamond particles through chipping, breakage,

etc.) so that with time the desired contoured shape is lost and the electrode must be replaced. If grinding pressures are avoided, and only the very light pressure needed for film removal is used, then the electrode and the insulating spacers will have very long lif Turning now to the electrolyte system, I use the sys tern usually provided with grinding machines for supplying coolant to the work area. Thus, as shown in Fig. 1, I provide a sump or supply tank 243, which may be provided with mechanical agitators 20a, 9. pump 21, a

tube or conduit 22, and a nozzle 23 adjacent the work area. Around the moving electrode I place a shroud 24 which collects the electrolyte and returns it to the sump or supply tank through conduit 25. The conduits, of course, should be made of material not readily corroded by the kind of electrolyte used.

As electrolyte I have used both acid and alkali solutions but these present some problems because the operator, particularly when doing off-hand grinding, will necessarily be splattered by the electrolyte. On this account, salt solutions which are neutral or nearly so are of some advantage. I have used with considerable success a solution made in the proportion of three ounces sodium nitrate and one and one-half ounce sodium acetate to one gallon of water. While a large variety of conductive electrolyte solutions can be used, I have found that the addition of a salt of the formic acid series, such as sodium acetate, sodium citrate, sodium tartrate, etc., is very helpful in preventing loading up of the electrode in the spaces between the insulating spacers when these are mounted permanently on the electrode.

The fiow of electrolyte to the work area itself is aided by the relative motion between the electrode and the material, and by the use of insulating spacers which provide a labyrinth of openings in which electrolyte is entrained and carried into and out of the work area, at the same time being violently agitated. The fiow of electrolyte for shaping of ordinary industrial cutting tools should be at the rate of about one liter per minute. In any case, the general flow rate should be adjusted upward until no further increase in current is occasioned by a greater rate of flow. The relative motion between the electrode and the material is not critical when insulating spacers are used, for the insulating spacers are so helpful in carrying electrolyte through the work area that it is not necessary to use extremely high motion. For example, I have varied the speed of rotation of a six inch diameter wheel electrode from 900 R. P. M. to 2400 R. P. M. which speeds are obtainable with the commonly used grinding equipment previously mentioned.

The electrical system represents another important aspect of my invention, for it makes it possible to supply current for the electrolytic process at the maximum level which may be used without causing excessive sparking or arcing through the electrolyte. It is possible, of course, to remove material by sparking or arcing, and some systems have been proposed which depend either entirely or in large part upon sparks or arcs for material removal. If prefer, however, to rely in large measure upon electrolytic action, but if the rate of material removal is to be satisfactory, it is desirable to use the maximum current which can be carried without breaking over into a degree of sparking or arcing which will be deleterious. The current may, of course, be controlled by a rheostat which is adjusted manually, for with the uniform spacing brought about by the use of insulating spacers, the resistance of the electrolytic circuit will not change very rapidly when a work piece of given size is being shaped. However, one work piece will be dilferent in area from others. Moreover, the resistance path will change as shaping proceeds and may change very rapidly in the case of oil-hand grinding where the work piece is placed in different positions with respect to the electrode. Under these circumstances, manual adjustment for maximum current becomes difficult, and accordingly the tendency is to reduce the current below the maximum that might otherwise be used, thus slowing down the rate of material removal.

The electrical system which I use, when combined with the uniform spacing achieved by use of insulating spacers, gives excellent results, although it may also be of value without the insulating spacers.

The general principle of operation is the use of any alternating current component which arises in the electrolytic circuit as the result of sparking or arcing to provide a signal for control apparatus which will reduce the supply voltage under these conditions.

While I have used a rectifier system, the same principle of operation may be applied to a motor generator system or to other supply means. If a motor generator system is used, 1 control the field of the motor generator, reducing the field strength in order to cut down the current supply when serious sparking occurs.

Referring to Fig. l, I provide a tapped line transformer accommodate a variety of available line voltages without the need for a variety of internal circuit components. As shown here, a three-phase system is employed, but it will readily be seen that the same system may be applied to a single phase or a two-phase s stem by adaptations which will be readily understood.

in the supply lines leading from line transformer 82, i provide saturable iron core reactance coils 84. The main windings have low resistance, and when their iron cores are saturated, pass the line voltage with little loss. The cores are saturated to greater or less degree by bias windings 36, the bias level being adjustable by potentiometer 122. The current is then passed through voltage reducing transformer 90 and through the rectifier system comprising rectifier elements 92. to the electrolytic circuit proper which consists of supply lines 94, brush 32, movable electrode 10, the electrolyte, the work piece 17 and 17a, and the tool holder 10. The brush 32 is held by spring 33 against the movable electrode 10. The spring 33 may be mounted on any suitable insulating holder 34. if desired, a plurality of brushes may be used.

In one of the supply lines 94 a shunt resistor 96 is provided across which the control signal is generated.

This control signal is fed to transformer 98 and then amplified by triode The output of triode is connected through a cathode follower tube Th2 to a high pass filter comprising inductance lil i, condensers tee and 1%, and resistor 110. The components of this filter are designed to provide sharp attenuation below 1500 cycles per second and minimum attenuation above this frequency. This is done in order that alternating current supply ripple in the electrolytic circuit will not have etfect on the control apparatus.

The filtered signal is then passed through transformer 112, germanium rectifier 13d, and is partially integrated by condenser iii and fed from potentiometer 118 to the control grid of pentode 12d. Potentiometer 118 adjusts the gain or sensitivity of the control system. Ordinarily, it is set so to cause supply voltage attenuation when the slightest incipient sparking is observed between electrode if) and the work piece 1''] and 17a. At this level, the sparks appear as fine hair-like strands and contribute little to current conduction or to the removal of material. However, adjustment may be made so as to produce somewhat heavier sparking with some increase in rate of material removal which, however, tends to produce a rough finish on the work piece and causes erosion of the electrode. it may be desired, nevertheless, to operate at this level for rough shaping and then to adjust to a lower level for finishing.

When adjusted at the minimum sparking level, the finish achieved may be as fine, when measured by 6. Brush analyzer, as live micro-inches R. M. S.

The output of pentode 12 3 is connected to control windings 8:3 which augment the fiux produced by bias windings 86. Normally the out ut of pentode 12% is sufficient to energize control windings to such an eX- tent that a substantial degree of saturation of the iron cores of reactance coils 34 exists. In response to signal, the output of pentode 128 is reduced, thereby reducing the degree of saturation of the iron cores of reactance coils 84. Under these conditions the effective inductance increases and the current passed is reduced; The level to 'P'alatu'S for Cutting; Shaping and g i q t s this which the current falls may be set by the adjustment of i on been shown dd w be n potentiometer 122 which controls current supply to bias 138mm ,that numerous modlficallons and Valuation? i windings 86. The lower the current supplied to bias y t 'i Without dfipaflilng 5mm y windings 86, the lower will be the minimum s;

of the order of .001 inch, 21 current density of sev ,fi 5 nciples of the invention. It is therefore desired by following claims to include within the scope of the vention all such variations and modifications by which of iron cores of reactance coils 84-, and accordingly, lower the current will be dropped in response to signal enerated by oscillations caused by Sparking or arcing. subsmfliiuy the few-k5 this Invention y 173 The l t i Supply system f the contra: filaments tamed through the use of substantially the same or described is a conventional half-wave 5r sv 19 s.

with a voltage doubler circuit for B supply for pentode as new and desire to secure by Letters 120. It consists of transformer 124, rectifiers lZiS and Patent 155 128, and condensers 1349, 132 and 134. l. Apparatus for combined el ctrolytic aria abrasive Wi h Space bgtw'ggn the electrode and the Wsrk niece sha 'ne of an electrically conductive workpiece includcornbination, a rotatable electrode having a wo kce made of an electrically conductive material, 3 connected to said electrode for rotating the lataid hundred amperes per square inch is achieved at vol between two and thirty volts, which is well Within t e range of usability without requiring special insulation to protect personnel from serious electrical shock.

When seen in normal operation, a slight "mount of 29 sparkin can usually be observed at the tra ing edge to and P 'ectin from said working face on cf the work pie e. The color of the spark will be a pale Sheri i @Qififmlflfi 9 5 disiaflFi blue, or it may be of reddi h a t or some other Cast said electrode and the workpiece, slid abrasive ins depending perhaps upon the electrolyte and the material H 8 Spacing In having 013611 sliaceibiideeil 5 P being worked. This is to be distinguished from arcing, 29 ($53 315? $95 l0 leave llflllilsillatsc P War in which a brilliant whiteblue light is cle-rly visible. 511395335 tQWFlTG WGTKPIBCB and Pl Frequently th arc i accompanied with a mnsidembifi means to entrain carry: fresh electrolyte into amount of popping and hissing noise, while such spa kfi adlacem P P398113 f9? P ing can not be heard above the noise of the machinery 1.113 haw/gen Said Wclking i533 311d i113 l a h and surrounding equipment in a machine shop environ- 30 m: 19W Current 3 5613365 to 1113K; SE

ment. Vfhile arcing under these conditions tends to be Wsmmg 5393 a caihsdeg l j b3 somewhat irregular and i t itt nh l arc moved from the worripiece by a comn nanon elccis characterized by steadier oscillation as seen in an osciltrail/tic attack and concul'licfit aoffisloil the P Q loscope than that produced by sparking. I find that I get M PP Pomblfiad elecfl'slyilc a1 1d b s b t results b dj i m current Supply with reign-Sn OD or an electrically conductive workpiece includto the size of insulating s acers used and the size of mg 3031511133033 a rotatable electrod? made offflm the work ie SQ th t Same ammmt f Sparking may electrically conductive material and having a working seen, but no arcing. For fine finish, but with somewhat POWEI means connectfid.m Said l ,for,rotat slower removal rate, I set the adjustments so that soar mg the 12mg: means for flowing a cOnGU-CnVe eleclmlyi'z 4 ra w 1L l l mg is ust barely visible at infrequent in ervals. Gr 0 ggi i g t 225 3225535 t lii giosg l ts r *l" ere g- C E l halted i @IFTVF ing from said working face not substantially more than W ich any sparsrng occurs LO glvc a very nne nrnsn. h d a O a it a bt n The electrolytic action is concentrated almost entirelji if 3 ii iig i jg g ys; r? F r 1 A I erecmo e an e I it r at n 1 es eon the sd-rfvacs the Walk i fading Lha vlectrbdu bjl 4' n spa ed from one another to leave unoccluded at least a very Shgflt amOun-t P maienal rfimoval also may Occur on e ua rter of sai when face wh ch is ex osed toward on the surfaces ad oining the surface being shaped for tha gvork g' p z between said pgrficles beiqg a distance of as much as A inch back from the surface ag a 5 fl freqh elnctroiyfp into the presented to the electrode. Under some circumstances z l s ane r i a meal; for paw '[lfilS 1S undesirable, and Where this is the case, I insulate mg g said el'ectrode theworknigce an electgic t e work niec or ex m le r so v 1 t H d a g that, ,3? current at a current density of not less than 200 amperes 6 6c nca y a L 9 smaces f f per square inch, with a voltage in the range between 2 and tgward electrod Ln I can obtam wry volts and in a sense to make said electrode a cathode,

ar e s I P e c I h b b L a 1 whereby material may be removed from the workpiece by n opera Sen 3 p matena from a combination of electrolytic attack and concurrent abrahard substances such as tungsten carbide at a rate comsion of the workpipce v r r l V g g i i l 1 iifi f 3. Apparatus for combined electrolytic and abrasive .lamon a F' 1 E O i shaping of an electrically conductive workpiece including 18 very great as neither tne electrode nor the insulating in ombinafion a rotatablg e1e,.tmde made an dec L L. s a V e spacers Tneed belwsrn l x by ubsa'amlal grindbng Pres trically conductive material and having a working face,

r,- r AA A C v o sures a so l L 21 Fans 01 using f i power means connected to said electrode for rotating other than diamonds as insulating spacers, thus making the latter means for flowin an electrolyte over said it possible to produce lower cost grinding Wheels. The c f fi h o d b 11 1 working face, hard, abrasive, electrically insulating spac- A 4 l L A v J I sur ace ms on Pleres Join mg means fixed to and pro ecting from said Working d apparatus be macle evfin better i that i face not substantially more than .005 inch to determine narlly obtained-in commercial. diamond abrasive practice, Spacing distancg betwgen said electrode and the Work The entire apparatus is safe and easy for operators of niece, Said abrasive insulating Spacing means h i normal skill to use. The whole system and apparatus a therein l i j l d portions f id y be adapted to e-Xisting grinding equillmeni by P wbrking face exposed toward the workpiece and providvidlilg electmde of i kiltld here described and ing means to entrain and carry fresh electrolyte ihto the l g throllgh an to an @Xlst work space adjacent the workpiece, means for passing 2 grlndmg spmdle, by subsmutlng an 616m 7 7601 between said electrode and the workpiece a high density,

the Ordinary 2 and y PYOVidiJg the low voltage current in a sense to make said electrode electrlcal appflfaills In 0118 Or 1110fa Convenient p g a cathode, and automatic means connected to said current passing means for preventing arcing across the space While a preferred embodiment of the method and ap- 7 between the electrode and the workpiece established by said abrasive spacing means.

4. Apparatus for combined electrolytic and abrasive shaping of an electrically conductive workpiece including in combination, a rotatable electrode made from electrically conductive material and having a working face, power means connected to said electrode for rotating the latter, means for flowing an electrolyte over said working face, hard, abrasive, electrically insulating spacing means consisting of a large number of spaced abrasive insulating particles fixed to and projecting from said working face not substantially more than .005 inch to determine spacing distance between said electrode and the workpiece, said abrasive insulating spacing means having open spaces between the particles thereof, to leave uninsulated portions of said working face exposed toward the workpiece and providing means to entrain and carry fresh electrolyte into the work space adjacent the workpiece, means for passing between said working face and the workpiece a high density current in a sense to make said working face a cathode, and means connected to said current passing means for controlling the voltage of such current to that just below which arcing would occur between said working face and the workpiece across the spacing distance established by said abrasive spacing L1 means.

5. Apparatus for combined electrolytic and abrasive shaping of an electrically conductive workpiece including in combination, a rotatable electrode having a working face made of an electrically conductive material, means connected to said electrode for rotating the latter, means for flowing a conductive electrolyte over said working face, electrically insulating spacing means consisting of insulating abrasive elements fixed to said electrode and projecting above the working fact thereof only a very short distance to determine the spacing distance between said electrode and the workpiece, said abrasive insulating spacing elements being laterally spaced to leave uninsulated portions of said working face exposed toward the workpiece and providing means to entrain and carry fresh electrolyte into the work space adjacent the workpiece, and means for passing between said working face and the workpiece a high density, low voltage current in a sense to make said working face a cathode, whereby material may be removed from the workpiece by a combination of electrolytic attack and concurrent abrasion of the workpiece.

6. Apparatus for combined electrolytic and abrasive shaping of an electrically conductive workpiece including in combination, a rotatable electrode made of an electrically conductive material and having a working face, power means connected to said electrode for rotating the latter, means for flowing an electrolyte over said working face, hard, abrasive, electrically insulating spacing means fixed to and projecting from said working face not substantially more than .005 inch to determine spacing distance between said electrode and the workpiece, said abrasive insulating means having openings therein leaving uninsulated portions of said working face exposed toward the workpiece and providing means to entrain and carry fresh electrolyte into the work space adjacent the workpiece, current supply means operatively connected to the workpiece and said electrode for passing between the workpiece and said electrode across the work space therebetween a high density, low voltage current in a sense to make said electrode a cathode, and control means responsive to spark generated alternating current components in said current supply means arising from sparking between said electrode and the workpiece for limiting the supply of current.

7. Apparatus for electrolytically assisted grinding of a conductive workpiece comprising in combination, a

grinding wheel having a conductive matrix, having a working surface and having nonconductive particles of diamond bort protruding therefrom not more than .005

inch, means mounting said grinding wheel'rotatably about its axis, power means for rotating said grinding wheel, support means for supporting a conductive workpiece opposite said working surface for movement toward said working surface, said support means being adapted to make electrical contact with the workpiece, means for conducting electricity respectively to said grinding wheel and to said support means, insulating means interposed between said grinding wheel and said support means, means for supplying a substantially continuous low voltage direct current across said support means and said grinding wheel in a sense to make said grinding wheel a cathode, and means for delivering a conductive fluid electrolyte over said working surface, whereby an electrolytic circuit is established between said grinding wheel and a workpiece when the workpiece supported by said support means is moved into contact with said abrasive particles.

8. In combination a rotatable electrode grinding wheel having an electro-conductive working face, numerous small hard abrasive insulating particles fixed to said grinding wheel and protruding above the working face thereof not more than .005 inch, means for flowing a conductive electrolyte over the working face of the electrode, support means for holding a workpiece against said numerous abrasive particles and in close proximity to the working face, and means for causing an electric current to flow through the electrolyte and between the electrode grinding wheel and the workpiece in a sense to make the workpiece an anode.

9. The combination claimed in claim 8, including power means for causing relative oscillatory movement between the workpiece and said rotatable electrode grinding wheel.

10. The combination claim in claim 8, including power means connected to the workpiece to hold the workpiece against the particles protruding above the working face of said rotatable electrode grinding wheel.

11. The combination claimed in claim 8, including pneumatic means connected to the workpiece to urge and hold the workpiece against the particles protruding above the working face of said rotatable electrode grinding wheel.

12. The combination claimed in claim 8 including power means connected to the workpiece to urge and hold the workpiece against the particles protruding above the workingtface of said rotatable electrode grinding wheel, and other power means for causing relative oscillatory movement between the workpiece and said rotatable electrode grinding wheel.

13. The combination claimed in claim 8, including a coating of an electrically nonconductive lacquer on the workpiece to be shaped adjacent and surrounding the active face thereof to prevent passage of current between the workpiece and said rotatable electrode grinding wheel except at the active face of the workpiece.

14. In combination a rotatable electrode grinding wheel having an electro-conductive working face, diamond bort fixed to said grinding wheel and protruding above the working face thereof not more than .005 inch, means for flowing an electrolyte over the working face of the electrode, support means for holding a workpiece against said diamond bort and in close proximity to the working face, and means for causing an electric current to fiow through the electrolyte and between the electrode grinding wheel and the workpiece in a sense to make the workpiece ananode.

15. In combination, a rotatable electrode grinding wheel having a metallic working face, numerous, small, hard, insulating abrasive particles fixed to said grinding wheel and protruding above the metallic working face thereof not more than .005 inch, said numerous abrasive particles being spaced from one another to leave unoccluded portions of the working face to provide direct electrolytic paths between the working face and a workjection of the particles above the working ductive workpiece by abrasion and electrolysis, the steps which include bringing the workpiece from which material is to be removed into close spacial relationship to the working face of a movable conductive electrode having numerous abrasive particles fixed to and projecting from the working face thereof not more than .005 inch so that the gap between the workpiece and the working face of the electrode is not greater than .005 inch, providing rapid relative movement between the. electrode and the workpiece, supplying a conductive electrolyte between the electrode and the. workpiece at a rapid rate of flow,

. and impressing an electric current of high current density and at a low voltage between the surface of the workpiece from which material is to be removed and the electrode in a sense to make the electrode a cathode, but without arcing between the workpiece and the electrode.

17. in the electrolytic process of removing material from a conductive workpiece by means of a movable electrode having a conductive working face to which numerous hard abrasive insulating particles are afiixed to project therefrom, the steps which include limiting the proface of the electrode to not more than .005 inch, bringing the workpiece against the particles so that there is a gap between the workpiece and the working face of the electrode not greater than .005 inch, supplying an electrolyte between the working face of the electrode and the workpiece at a rapid rate of flow, and impressing an electric current of a current density not less than 200 amperes per square inch between the surface of the workpiece from'which material is to be removed and the working face of the electrode in a sense to make the electrode a cathode but without arcing between the workpiece and the electrode.

18. In the electrolytic process of removing material from a tungsten carbide workpiece by means of a movable electrode having a conductive working face to which numerous hard abrasive insulating particles are afiixed to project therefrom, the steps which include limiting the projection of the particles above the working face of the electrode to not more than .005 inch, bringing the workpiece against the particles so that there is a gap between the workpiece and the working face of the electrode not greater than .005 inch, supplying an electrolyte comprising a water solution of a salt of a strong acid and a salt capable of complexing with tungsten between the work- 'ing face of the electrode and the workpiece at a rapidrate .of flow, and impressing an electric current of a current density not less than 200 amperes per square inch between the surface of the workpiece from which material is to be removed and the working face of the electrode in a sense to make the electrode a cathode but without arcing between the workpiece and the electrode.

Cited in the file of this patent UNETED STATES PATENTS 1,017,671 Jenkins Feb. 20, 1912 1,098,338 Thompson May 26, 1914 1,273,432 Weeks July 23, 1918 1,362,159 Weeks Dec. 14, 1920 1,376,366 Wertheimer Apr. 26, 1921 1,598,731 Lee Sept. 7, 1926 1,864,490 Harrison June 21, 1932 1,913,962 Sharples June 13, 1933 1,994,762 Ennis Mar. 19, 1935 2,320,495 Waterman June 1, 1943 2,385,198 Engle Sept.'18, 1945 2,387,313 Wilson Oct. 23, 1945 2,526,423 Rudortf Oct. 17, 1950 2,539,455 Mazia Jan. 30, 1951 FORElGlI PATENTS 3,087 Great Britain of 1904 OTHER REFERENCES Pirani et al.: Zeitschrift fiir Metallkunde, vol. 16 (1924), pages 132, 133.

B. N. Zolotykh: Sharpening of Cemented Carbide Tools by the Electro-Erosion Spark Discharge Process, Stanki i Instrument, v. 18, #3, pages 23-4 (1947).

S. E. Noskov: Electrolytic Tool Sharpening, Stanki i Instrument, v. 19, #10, pages 202 (October 1948).

Electrolytic Cutting of Metal, Promyshlennya Energetika, #1, p. 11, (January 1946); Engineers Digest, v. #10, p. 498 (1946); abstracted in Monthly Review,

A. E. S. p. 1057 (September 1947). V 

1. APPARATUS FOR COMBINED ELECTROLYTIC AND ABRASIVE SHAPING OF AN ELECTRICALLY CONDUCTIVE WORKPIECE INCLUDING IN COMBINATION, A ROTATABLE ELECTRODE HAVING A WORKING FACE MADE OF AN ELECTRICALLY CONDUCTIVE MATERIAL MEANS CONNECTED TO SAID ELECTRODE FOR ROTATING THE LATTER, MEANS FOR FLOWING A CONDUCTIVE ELECTROYTE OVER SAID WORKING FACE, ELECTRICALLY INSULATING SPACING MEANS CONSISTING OF APRTICLES OF INSULATING ABRASIVE MATERIAL FIXED TO AND PROJECTING FROM SAID WORKING FACE ONLY A VERY SHORT DISTANCE TO DETERMINE THE SPACING DISTANCE BETWEEN SAID ELECTRODE AND THE WORKPIECE, SAID ABRASIVE INSULATING SPACING MEANS HAVING OPEN SPACES BETWEEN THE PARTICLES THEREOF TO LEAVE UNINSULATED PORTIONS OF SAID WORKING FACE EXPOSED TOWARD THE WORKPIECE AND PROVIDING MEANS TO ENTRAIN AND CARRY FRESH ELECTRLYTE INTO THE WORK SPACE ADJACENT THE WORKPIECE, AND MEANS FOR PASSING BETWEEN SAID WORKING FACE AND THE WORKPIECE A HIGH DENSITY, LOW VOLTAGE CURRENT IN A SENSE TO MAKE SAID WORKING FACE A CATHODE, WHEREBY MATERIAL MAY BE ELECTROLYTIC ATTACK AND CONCURRENT ABRASION OF THE WORKPIECE. 